The present application relates to a light-transmissive film having a cubic structure on each of front and back surfaces thereof, a manufacturing method therefor, and a display apparatus incorporating the light-transmissive film therein.
In recent years, liquid crystal display apparatuses are replacing CRTs (Cathode Ray Tubes) which have been the predominant display apparatuses owing to their advantages such as low power consumption and space-saving design, increasingly lower prices, and the like.
The liquid crystal display apparatuses are classified, by, e.g., illumination methods for displaying images, into several types, a typical one of which is a transmissive-type liquid crystal display apparatus that displays images by utilizing a light source arranged behind a liquid crystal panel.
In such a display apparatus, it is very important to increase display luminance with decreasing power consumption in enhancing the product value. Accordingly, it has been strongly desired to increase a gain of an optical system arranged between the liquid crystal panel and the light source, while minimizing the power consumption of the light source.
For example, in Japanese Patent No. 3158555 (Patent Document 1), a technology is disclosed in which a light-transmissive film called a brightness enhancement film is arranged between a liquid crystal panel and a light source. In this light-transmissive film, e.g., right-angled isosceles triangular prisms each having a vertical angle of 90 degrees are arranged parallel to a surface (front surface) on a light emergent side, whereas a surface (back surface) on a light incident side is flat.
However, in the light-transmissive film described in Patent Document 1, when the light-transmissive film flexes due to the influence of heat or the like, the back surface may in some cases be stuck to a member (e.g., an optical film disposed between the light-transmissive film and the light source) disposed on a back surface side. When the back surface is stuck to the other member in this way, optical phenomena called “Newton's rings” and “wet-out” occur. Furthermore, when right-angled isosceles triangular prisms each having a vertical angle of 90 degrees are arranged, light is converged greatly toward the front, thereby causing the abrupt reduction in the viewing-angle dependence of the brightness called dark band, cut-off, and the like.
Thus, in order to decrease such phenomena (non-uniformity due to interference), as disclosed in Published Translation of International Patent Application No. 2001-524225, a technique is considered in which protrusions are disposed on the back surface to decrease an area of contact with another member. However, when the protrusions are disposed on the back surface simply, light component available for convergence by the prisms decreases compared with when the back surface is flat, thereby reducing the front luminance.
Furthermore, in order to ease the abrupt reduction of the viewing angle dependence of brightness, a technique is considered in which protrusions are disposed on the back surface similarly to the above or in which the vertex of each prism formed on the front surface is curved. However, in this technique, light component available for convergence by the prisms decreases compared with when the back surface is flat, thereby reducing the front luminance. In addition, when the vertices are curved, the convergence effect by the prisms themselves is lost, thereby reducing the front luminance.